Portable hand tool

ABSTRACT

A small portable air tool having a tubular housing, a rotary air motor mounted to reciprocate in the housing and receiving air under pressure from the expansible chamber formed between the motor and the rear wall of the housing, and a spring at the front of the housing for forcing the air motor rearwardly when the air supply is cut off. The novel tool provides a novel method for choking and quickly decelerating the rotor shaft while simultaneously causing exhausting of air from said expansible chamber through said motor, thereby providing maximum protection against tool breakage and preventing dirty air from being sucked into said motor.

United States Patent [72] Inventor Herman C. Tuttle I [56] ReferencesCited 26720 White Way Drive, Richmond UNITED 17 T PATENTS v 21 A 1 N $13 2,657,595 11/1953 ,Shaff 77/335 f july'ls 1969 2,865,236 12/1958'Parke 77/335 [45] Patented Aug, 1971 2,88l-,589 4/l959 Hm et al l73/l58Primary Examiner-Emest R. Purser I Attorney-McCoy, Greene & HowellABSTRACT: A small portable air tool having a tubular housv ing, a rotaryair motor mounted to reciprocate in the housing and receiving air underpressure from the expansible chamber [54] ig g fonned between'the' motorand the rear wall of the housing, n g and a spring at the front of thehousing'for forcing the air [52] US. Cl 173]], motor rearwardly when theairsupply is cut off. The novel tool '77/33L5, l73/l55, 173/ l 63, 418/1provides a novel method for choking and quickly decelerating [51] Int.Cl B24b-17/00, the rotor shaft while simultaneously-causing exhaustingof air B23b 45/04 from. said expansible chamber through'said motor,thereby [50] Field of Search 77/315; providing maximum protectionagainst tool breakage and v preventing dirty air from being sucked intosaid motor.

PATENIED AUBBI l97| INVENTOR. HERMAN 6. 71/7725 N mm m an? & Q G Q mm mwvb mm m MW 0 w w m k m .0 3%! NW l 8mm 0W m, wll Wm M\ l mm \m t mm .w\w mm 9w ATTORNEYS PORTABLE HAND TOOL DESCRIPTION OF THE INVENTION Thepresent invention relates to small portable rotary air tools adapted tobe held in one hand to effect manual cutting, grinding or finishingoperations and more particularly to an air tool having a novelreciprocating arrangement to effect rapid deceleration of the rotorshaft and to prevent dirty air from being sucked into the motor.

For many years there has been extensive use of small portable rotarypneumatic tools which rotate at speeds in excess of 20,000 revolutionsper minute. These tools have tended to wear out rapidly at such highspeeds, especially when used in foundries and other dirty atmospheres,but they have nevertheless been considered superior to other types ofportable equipment for the particular purpose. Although wear remained aserious problem it was not an insuperable one because of the specialconstruction of the air tools to permit quick rebuilding or replacementof the air motors.

In order to be acceptable commercially, rotary air tools must not onlyhave provision for quick and simple replacement of tools and quickreplacement of worn motor parts, but must also be small, compact andlight in weight so that they can easily be operated by one hand. Addedaccessories such as brakes and tool guards which were not absolutelynecessary and which added materially to the size and weight of the toolor made it more difficult to operate were not considered acceptable andwere not used. Thus, conventional air tools were not provided withbrakes and continued to rotate for substantial periods of time after theair supply was shut off due to the inertia of the parts. Such rotationcaused the air motors to act as suction pumps and to draw in air ladenwith dirt or abrasive material, thereby causing rapid wear. especiallybecause of the extremely high rotational speeds e.g., 20,000 rpm. orhigher). This problem has existed for more than a decade but no one hada practical solution to the problem.

Brakes to stop rotation of the rotor shaft did not provide a solution tothis problem for various reasons. A brake which caused a sudden stop wasnot acceptable because of shock damage to the tools and the danger oftool fracture at speeds in the neighborhood of 20,000 revolutions perminute. Slower stops could avoid such shocks but would not preventoperation of the air motor as a suction pump for brief periods of timeand could not prevent dirt from being sucked into the motor. Furthermoreit was not known, prior to this invention, how to provide a reliablebrake which would be effective and commercially acceptable on a smallrotary air tool of the type commonly used.

The present invention involves the discovery of a basically new methodfor solving the wear problem in rotary air motors and a new portable airtool having essentially all the ad vantages of the presently used airtools as set forth above, such as small size, quick tool replacement,easy motor replacement, ete.,-and also having novel means for providingchoking and cushioned stopping of the rotor shaft while simultaneouslypreventing dirty air from being sucked into the motor. The new method ofstopping rotation of the rotary air motor not only provides anexceptional solution to the dirt and wear problem but also providesmaximum protection for the grinding wheel, deburring tool or other toolbeing used, thus making it feasible to use rotational speeds which haveheretofore been considered excessive or to employ diamond tools, carbidetools and other grinding or cutting tools which are not in use today onportable air tools because of their expense and/or their fragile orbrittle nature.

The process of this invention is unusual in that the air motor is movedaxially in its tubular housing by a strong spring to stop the rotation.For some reason, when an air chamber is provided adjacent the motor andthe air therein is rapidly compressed by the axial movement to force airthrough the air motor, the rotor quickly decelerates and stops rotating.This is a cushioned stop free of shocks which could damage the equipmentor cause tool breakage. Because the air is forced out the motor exhaustduring the deceleratiomthe motor does not suck dirt into the motor andwear of the parts is minimized. The air motor will, therefore, have along life even when used in a dirty atmosphere.

The air tool of the present invention is only slightly larger than aconventional rotary air tool and can readily by supported and operatedby one hand. It has a closed tubular housing, preferably with a diameterof l inch to 2 inches and a length of 4 to 8 and has a rotary air motorwith a piston stator mounted to slide axially in the housing, wherebyanexpansible air chamber is formed at the rear of the housing. Toolgripping means, such as a conventional collet, maybe mounted on the endof the rotor shaft, and a conventional manual control valve may beprovided at therear of the housing to control the admission of air tosaid expansible chamber and said motor. Means are provided forautomatically causing a cushioned deceleration and stopping of the rotorshaft comprising a powerful spring means at the front of the housingbiasing the stator rearwardly. When the control valve is opened to admitair to the rear of the housing, the air in the expansible chamber entersthe inlet of the air motor and the air pressure causes the stator tomove axially to its advanced operating position while compressing thespring. A strong spring is required to prevent forward acceleration ofthe tool at a dangerous rate. The air from said chamber passes from theinlet to the exhaust of the motor to drive the motor at a high speed,such as 20,000 rpm. or higher.

When the control valve is shut off, as by releasing the handle, thespring moves the entire air motor rearwardly to compress the air trappedat the rear of the housing and to cause partial blocking of the motorexhaust ports. This causes the air trapped in the housing to movethrough the air motor to the exhaust and surprisingly effects rapiddeceleration and stopping of the rotor shaft rotation. Because of theabsence of shock during deceleration, the novel process of thisinvention is well suited for the air motors of grinders whose grindingwheels are subjected to extremely high centrifugal forces and,therefore, cannot tolerate shocks due to sudden stops.

An object of the present invention is to provide a small compact rotaryair tool with essentially all of the advantages of commonly used rotaryair tools but which has a greater useful life and provides moreprotection against damage to the tool and injury to the operator.

A further object of the invention is to minimize wear in rotary airtools by preventing operation of the air motor as a suction pump to drawdirt into the motor.

A still further object of the invention is to provide reliable cushionedstopping of a rotary air motor which does not create objectionableshocks or cause dangerous tool fractures.

Another object of the invention is to reduce the hazards to the operatorby stopping rotation of the tool and retracting it so that it cannoteasily be broken when not in use.

Another object is to provide a simple rotary air tool that can beassembled and disassembled readily, that permits rapid replacement oftools or grinding wheels, that is of the proper size for operation byone hand, and that provides economical, safe, reliable operation withminimum maintenance costs.

These and other objects, uses and advantages of the invention willbecome apparent to those skilled in the art from the drawings,description and claims which follows. In the drawings:

F IG. 1 is a vertical sectional view of an air tool constructedaccording to the present invention, the parts being shown in theirpositions when the grinding tool is in its advanced operating position;

FIG. 2 is a vertical sectional view taken on the line 2-2 of FIG. 1;

FIG. 3 is a vertical sectional view looking at the end of the air motor;and

F IG. 4 is a foreshortened fragmentary side elevational view of the airtool when the supply of air is discontinued with the grinding tool heldin its advanced position by a special tool to permit placing of a wrenchon the collet body. Referring more particularly to the drawings, whichare drawn substantially to scale and in which like parts are identifiedby the same numerals throughout the several views, FIGS. 1 to 4 show asmall hand-supported portable air tool A constructed according to thepresent invention and having a piston like air motor 8 mounted forreciprocation therein between the advanced position indicated in FIG. 1and a fully retracted position against the rear wall of the tubularhousing 1. The housing is preferably a closed cylindrical steel tubehaving a diameter of l inch to 2 inches and a length of 4 to 8 inchesand is adapted to be held in the hand of an operator gripping aconventional throttle lever 10. When the lever is depressed against theouter surface of the housing to open the control valve 9, high pressureair is admitted to the expansible chamber 2 at the rear of the housingand forces the air motor B against the helical return spring 3 tocompress the spring and advance the cutting or grinding tool 7 to anoperating position as shown in FIG. 1.

The spring 3 must be heavy and very strong to function properly and isstrong enough to prevent advancing movement of the air motor when theair pressure in chamber 2 is pounds per square inch or below. The springis constructed so that it can exert a force on the air motor equal tothat exerted by air in chamber 2 at a pressure of at least pounds persquare inch (preferably at least pounds per square inch).

The portable air tool of this invention is small and of light weight forease of operation. The tubular barrel or housing 1 is closed at the rearend and has a front portion 12 which is threaded to receive aninternally threaded cap 11 having an internal cylindrical surface 37coaxial with the smooth cylindrical internal surface of the housing.

As herein shown, the from half of the housing is thickened forwardly ofthe annular shoulder 17 and has an annular groove 14 of uniform widthwhich receives a split metal exhaust deflector 13 having flat end edges16 spaced apart as shown in FIG. 2. The housing has a series of radialexhaust ports 15 midway between the sides of the groove 14 forcommunication with the annular chamber 59 of the air motor B, and thedeflector 13 has an arcuate cross section to provide an annular space 38around the housing, whereby the exhaust air from the motor flows aroundthe groove 14 and discharges between the deflector edges 16 as indicatedby the arrows in FIG. 2. The operator may readily turn the deflector 13by sliding it in its groove 14 to change the location of the exhaustdischarge so that the motor will exhaust in the desired direction (i.e.,away from his body).

The housing 1 has a thin cylindrical portion l8 extending from theannular shoulder 17 to the thick rear portion 19, which has a flat face36 perpendicular to the axis of the housing and parallel to the flatrear piston face 47 of the air motor B for engaging the face 47 when thepiston like motor is retracted by its spring 3. The portion 19 has avertical cylindrical bore 20 and a counterbore 21 coaxial therewith witha tapered valve seat 28 therebetween. The counterbore is threaded toreceive a hollow screw plug 22, which supports a helical valve spring33.

A cylindrical passage 24 is formed in the portion 19 near the axis ofthe housing to provide communication between the ex pansible chamber 2and the lower portion of the bore 20, and a cylindrical inlet opening 23is provided in the portion 19 to provide communication between thecounterbore 21 and a flexible rubber air supply hose 25, which isconnected to an air pump, air tank or other conventional source of highpressure air (not shown). A conventional inlet connection is provided at26.

The flow of air from the hose 25 to the expansible chamber 2 is normallycutoff by a conventional control valve 9, which has an elastic rubberO-ring 29 sealingly engaging the valve seat 28. The valve may be openedby depressing a conventional throttle lever 10 which is pivotallymounted on the housing by a pivot pin 34. The lever engages the roundedupper end portion 32 of the valve stem. As herein shown, the controlvalve 9 comprises a cylindrical guide portion 31,

which slides in the bore 20, a tapered intermediate portion 27 with thesame diameter as the portion 31, a bottom portion 69 with a greaterdiameter, and a portion 30 between the portions 27 and 31 with adiameter which is reduced to facilitate airflow from the counterbore 21through the port 24 to the chamber 2. The circular O-ring 39 issupported in the annular groove between the portions 27 and 69 andfunctions to shut off the airflow when the throttle lever 10 is releasedso that the spring 33 can move the O-ring against the valve seat 28.

The portable tool of the present invention is unique in that thesliding-vane air motor is mounted for reciprocation, like a piston, andis rapidly decelerated and stopped by the action of the strong returnspring 3 when the throttle lever is released. However, the basicelements of the air motor used in the tool are conventional. It will beunderstood that conventional air motors of various types may be mountedfor reciprocation in an air tool constructed according to thisinvention. Conventional air motors are shown, for example, in thefollowing patents: 2,401,957; 2,423,957; 2,570,009; 2,575,524;2,575,640; 2,830,560 and 2,905,149.

The air motor B may have a conventional rotor and stator. As hereinshown the rotor 5 is mounted on the rotor shaft 6 coaxial therewith forrotation in unison with said shaft and has four sliding vanes 58 whichmay be urged outwardly against the internal cylindrical surface of .thestator by air pressure, springs or other conventional means. The statorcomprises a main cylinder 39 with an external cylindrical surface 40coaxial with the housing surface-35 and the rotor shaft 6 and aneccentric internal cylindrical surface 41 which engages the vanes 58.The main cylinder has a pair of inlet ports 42 connected by one or morelongitudinal passages 43 and has a series of conventionalcircumferentially elongated exhaust ports 44 which discharge into theannular chamber 59. The opposite ends of the cylinder 39 are closed byinternally threaded front and rear end caps 45 and 46 which screw ontothe externally threaded end portions of the main cylinder axiallyoutwardly of the ports 44. Conventional flat circular wear plates 48 and49 are provided at the front and rear of the cylinder 39 and are clampedagainst the ends of said cylinder by said end caps. The end caps providesupports for conventional front and rear bearings 50 and 51, whichsupport the rotor shaft 6 for rotation about the axis of the housing 1.It is preferable to provide a bearing spacer 52 between the wear plate48 and the shaft 6, but the wear plate 49 may be of a size to fit theshaft 6 if such spacer is omitted.

The end caps 45 and 46 are shaped to fit the wear plates 48 and 49 andthe outer races of the bearings 50 and 51 and may be of the same ordifferent shapes. Each has a smooth external surface with a diametersubstantially equal to the diameter of the housing surface 35 and isadapted to reciprocate like a piston. The cap 46 is externallycylindrical and has a flat end surface 47, whereas the cap 45 isspecially shaped to receive the return spring 3 and is preferablyspecially shaped to provide axial exhaust passages at 68. It contains noair passages, whereas the cap 46 has a cylindrical air inlet port 57axially aligned with the air inlet port 56 of the wear plate 49 to admitair to the inlet ports 42 of the air motor. The end cap 45 has a frontportion which fits the outer race of bearing 50 and extends axially intothe chamber and within the spring 3 and had a rear portion 66 which isinternally threaded to fit the threads of the main cylinder 39.

The preferable external shape of the end cap 45 is shown in F l6. 3. Theportion 66 of the cap has regularly spaced cylindrical surface portions67 and regularly spaced flat surface portions 68. The outer surface ofthe portion 66 is initially formed as a cylinder, like the outer surfaceof the other end cap 46, and with a diameter substantially equal to thatof the internal barrel surface 35. Circumferentially spaced portions ofsaid outer surface are then ground away at 68, leaving the portions 67.As herein shown, each surface 68 is flat and has a uniform width alongthe length of the portion 66. An optional exhaust air passage is thusformed in the assembled tool A at each surface 68 between the surface 35and the surface 68 leading from the exhaust chamber 59 to the chamber 70containing the spring 3. Part of the exhaust air from the motor B may,therefore, pass to the chamber 70 and out of the tool through theannular space between the collet body 53 and the surface 37. Thisoutward exhaust flow is preferred to keep the dirt out of the chamber 70during operation of the tool.

The inertia of the grinding or cutting tool 7, the rotor 5, and thecollet 8 tends to keep these parts rotatingwhen the control valve 9 isclosed, and it would be expected that the air motor would, therefore,tend to act as a suction pump to draw dirty air into the chamber 70 andinto the motor. However, in the tool of this invention this is avoidedbecause of the action of the strong spring 3 in conjunction with therestricted exhaust passages leading from the motor.

When the air supply is cut off by releasing the throttle lever 10, thereturn spring 3 rapidly moves the air motor toward the surface 36 toretract the tool 7. This moves'the portion 66 of the end cap 45 past theports and restricts the exhaust flow so that any air flowing to or fromthe exhaust chamber 59 of the motor must flow over the axial exhaustpassages at 68 or other restricted outlets which limit the airflowand,-therefore, yieldably resist the axial acceleration of the motortoward its retracted position For some reason, as the air is forced outof the chamber 2 through the motor to the exhaust passages at 68, therotation of the motor is rapidly decelerated and brought to a halt,usually in a period of less than one second. For example, in a typicalair tool constructed according according to this invention where the airmotor is rotated at a speed of 20,000 to 25,000 revolutions per minute,the contraction of the air chamber 2 during axial retraction of the airmotor by its spring 3 may be accompanied by a speed reduction of 10,000to 20,000 revolutions per minute in a period of I second or less. Thisis a cushioned deceleration which avoids dangerous shocks and avoidstool breakage.

The spring 3 will hold the air motor in its retracted position againstthe surface 36 so that the tool 7 is retracted within and protected bythe front cap 11. The external diameter of the tool 7 must, therefore,be less than the diameter of the surface 37 of such cap which is usuallyin the range of 0.5 to 1.0 inch. Where a grinding wheel is used at 7having a diameter of l to 1.15 inches, the cap 11 may be replaced withone having a surface 37 of greater diameter.

The collet 8 has an external cylindrical surface with a diameter lessthan that of the surface 37 and may be of a conventional type. As hereinshown the rotor shaft 6 has a onto the conventional split externallythreaded front portion V of the collet body.

Although the spring 3 is very strong and may require a force of 40 to 60pounds or more to efiect full compression of the spring, the tool 7 canbe held in an advanced position to permit tool replacement. This is doneby employing a special tool 60 illustrated in FIG. 4 which has a longthin portion 61 and a small end flange 62 shaped to fit against thecollet nut 54. If the surface 37 is not notched to receive the tool 60,the portions 61 and 62 must be small enough to fit between the surface37 and the outer surface of the collet 8 or the tool 7 so that the toolcan be inserted axially into the chamber 70 to a position wherein theflange 62 hooks onto and engages the bottom surface of the collet nut54. Then the tool 60 is moved axially relative to the tool A to compressthe spring 3. Preferably the tool 60 is clamped in a vise and the airtool is pulled away from the vise to expose the collet 8.

When the two straight tool-receiving grooves 63 of the collet body 53are exposed beyond the end of the cap 11, a conventional crescent wrenchw or similar tool can be placed on the grooves 63, and the tool 60 canbe removed because the wrench will engage the cap I I to preventexpansion of the spring 3. The wrench w is thus tightly held by thespring 3 against the cap 11. The nut 54 may then be unscrewed by asuitable wrench, and the shaft 64 of the grinding tool 7 may easily bewithdrawn. Thus it is simple to replace a worn or broken tool in a shortperiod of time. As soon as the tool is replaced, the wrench w is removedfrom the grooves 63 to release the collet body. The spring 3 thenreturns the air motor B to its retracted position against the surface36.

When using the special tool 60 and the wrench w to expose the collet 8in the manner described above, it is possible to change the cutting orgrinding tool 7 in less than I minute. if the tool 60 is not availablethe cutting tool may also be changed by removing the end cap 11 and thespring 3, but this takes a substantial amount of time. When the cap 11is removed, the air motor B can easily by removed from the cylindricalhousing 1.

The air tool of this invention is so far superior to the air toolsheretofore used that it may be considered a pioneer development. itsfantastic ability to stop rotation of the cutting tool in about 1 secondafter it is operating at a speed of over 20,000 revolutions per minutemakes the air tool ideal from the standpoint of cost of operation andalso from the standpoint of safety. This is particularly important whenthe tool is operated in a dirty atmosphere. In such atmosphere, the airtool of this invention minimizes wear and can be operated several timesas long without being overhauled.

The quick deceleration and cushioned stopping of the cutting tool notonly prevents dirt from being sucked into the air motor but also reducestool breakage. When a hard brittle cutting tool continues to rotate at10,000 r.p.m. or higher after the air supply to the motor is cut off, aslight impact on the end of the tool is apt to break it andresult in asharp projectile which can cause serious bodily harm to any person inthe vicinity. This type of breakage is common when using conventionalportable air tools, particularly when using hard' brittle cutting toolsof the type commonly used for deburring operations made of expensivetool steel.

Theportable air tool of this invention may be made in different size andshapes but is preferably provided with a generally cylindrical barrel orhousing having an internal cylindrical surface 35 with a diameter of 1inch to 2 inches. The air tool A shown herein has a diameter in theneighborhood of 1-1/2 inches an overall length in the neighborhood of 6inches. The rotor 5 of the air motor B has an axial length greater thanthe diameter of the internal surface 35 of the housing, and the airmotor moves axially in the housing, from its retracted positions againstthe surface 36 to its advanced operating position shown in FIG. 1, anaxial distance greater than said diameter and greater than the axiallength of said rotor. Such axial distance may be equal to or greaterthan'the axial length of the air motor B and is usually about 1.2 toabout 2 times the diameter of the surface 35 so that a large volume ofair is present in the expanded chamber 2. Such axial distance is atleast 1 inch and preferably at least 1.5 inches in any portable toolconstructed according to this invention. The retraction of the motor bythe strong return spring 3 forces this large volume of air through themotor to cause rapid deceleration and stopping of the motor in a shortperiod of time.

It will be understood that, in accordance with the provisions of thepatent statutes, variations and modifications of the specific devicesdisclosed herein may be made'without departing from the spirit of theinvention.

Having described my invention, I claim:

l. A process of operating a portable air tool having a housing, a rotaryair motor in said housing having a stator, a rotor, a rotor shaftadapted to project from said housing, an inlet opening for admitting airunder pressure to said motor, and

exhaust means for discharging the exhaust air from said motor, and meanson said shaft for supporting a grinding tool, said process comprisingadmitting air to said inlet opening and causing said rotor and saidshaft to rotate at a speed of at least 15,000 revolutions per minute,and cutting off the supply of said high pressure air to said motor todiscontinue operation of said motor, the improvement which comprises aa. providing an expansible air chamber with said inlet opening,

b. expanding said air chamber to a predetermined volume,

1 and c. contracting said air chamber to less than halfsuch volume whenthe supply of said high pressure air to said motor is cut off whilesimultaneously throttling ,said exhaust means to restrict andresist theflow from said air chamber so as to effect rapid deceleration of saidrotor shaft and to prevent a substantial amount of air from being suckedinto said motor. v 2. A process as defined in claim 1 wherein saidchamber is yieldable elastic means which yieldably resists expansion ofi said chamber by movement of said piston. I 3. A process as defined inclaim 1 wherein'said motor is mounted for reciprocation in a housing'andsaid chamber is expanded and'contracted by axial reciprocation of saidair motor.

-4. A process as defined in claim l wherein the air is admitted to saidinlet'opening at a pressure of 50 to 150 pounds per square inch.

-.6. A process as defined in claim5 whereinsaid air motor is Q roperated at a speed of at least 20,000 revolutions per minute when suchdeceleration is initiated. f I

7. A process as defined in claim 4 wherein the force applied to contractsaid air chamber during such deceleration is equal 8. A process ofoperating a portable grinder having ahousing, a rotary expansiblechamber air motor in said housing, 7 having a stator, a rotor, a rotorshaft having means supporting a grinding tool, inlet means for admittingair under pressure to said motor, and exhaust means for discharging theexhaust air from said motor; said process comprising mounting saidstator to slide" axially in said housing between an advanced operatingposition and a retracted position, whereby a closed expansible incommunication expanded and contracted automatically by a piston meansand motor to stop rotation immediately.

. 8 admittedto said motor, tool gripping means rigidly mounted on theend of said rotorshaft, control valve means for connecting the rear ofsaid housing to a source of air under pressure having a nonnal closedposition,-in which the flow of air to said expansible chamber and saidair motor is cut off, and an open position, in which air is admittedtosaid chamber to movethe motor to its advanced position and to effectdriving of the motor, and means for automatically causing a cushioneddeceleration of said air motor comprising throttling means forrestricting the exhaust of the motor after said valve means is moved tothe closed position and high-pressure spring return means for movingsaid stator rapidlylfrom said advanced position to said retractedposition to force the air from said expansible air chamber through therestricted exhaust of said motor to eflect rapid deceleration of saidrotor shaft and'to prevent a substantial amount of'air from being suckedinto said motor.

12;A portable air tool as defined in claim. 4 wherein said throttlingmeans chokes'the flow of exhaust gas from said air motor in response. toaxial retracting movement of the air is. A portable air tool as definedin claim 11 wherein said spring means applies a retracting forceequaltoat least 25 pounds per square inch.

14. A portable air tool as defined in claim 13 wherein said means forcausing deceleration of said air motor causes deceleration of the rotorshaft at a rate of at least 10,000 revolutions per minute persecondfl pv i v 15. A portable air tool as defined in claim 11 wherein saidcylindrical housing has exhaust ports which are located'near the middleportion of said pistonlike stator when the stator is air chamber isprovided on one side of the piston like stator at the rear of saidhousing in communication with the inlet of 'saidair motor, supplying airto air chamber at a pressure of to lSOpounds per square inch to causehigh speed rotation of th'efgrinding tool, anddiscontinuing the supplyofhigh pressure air to said motor while simultaneously causing a rapid vcushioned deceleration of said grinding too], said deceleration beingeffected by throttling said exhaust means to' choke and restrict theflow of exhaust air from said motor andmoving said stator rapidly fromsaid advanced to said retracted position to force the air from saidexpansible air chamber through the restricted exhaustof said motor tostop rotation of the rotor shaft and to prevent a substantial amount ofair from being sucked into said motor.

9. A process as defined in claim 8 where in the retracting force appliedto said pistonlike stator to cause the rapid deceleration'is equal to apressure of atleast 25 pounds per square inch.

10. A process as defined in claim 8'wherein the grinding tool isdecelerated at a rate of at least 10,000 revolutions per minute persecond.

11. A small portable air tool having a closed cylindrical housing with adiameter of 1 inch to 2 inches and a length of 4 to 8 inches adapted tobe held in the hand of an operator, 8 rotary expansible-chamber airmotor having a piston like stator mounted to slide axially in saidhousing between an advanced operating position and a retracted position,whereby an expansible air chamber is provided at the rear of saidhousing,

said air motor having inlet and exhaust openings" to-admit air underpressure from said expansible chamber and exhaust it through the statorto atmosphere and having a rotor shaft mounted for rotation coaxial withsaid housing and a rotor carried by said shaft which is driven by thepressure of the air in its advanced position and wherein said ports areclosedin response to movement of the stator to its retracted position tochoke the motor exhaust. v j

16.,A portable high speed pneumatic grinder (A) having a closed housing(1 a rotary expansible-chamber air motor (B) having a piston like stator(4') mounted to slide axially in said housing between an advancedoperating position and a retracted position, wherebyan'expansibleair'chamber (2) isprovided at the rear of said housing,said air motor having inlet and exhaust openings (42 and 44) to admitair under pressure from said expansible chamber and exhaust it throughthe stator to atmosphere and having a rotor shaft (6) mounted forrotation coaxial withsaidhousing and a rotor (5)carried by said shafthaving sliding vanes (58) driven by thev pressure of the air admittedtosaid motor, means (8) on the end of said rotor shaft for gripping agrinding tool (.7), control valve means (9) for connecting said housingto a source of air-under pressure having a normal closed position, inwhichthe flow of air to said expansible chamber and said air motor iscut off, and an open position, in which air under a pressure of 50 to150 pounds per square inch is admitted to said chamber to move the motorto its advanced position andto effect highspeed driving of the motor,and means for causing a cushioned deceleration of said air motor toeffect immediate stopping of tool rotation without causing. damage tothe grinding tool I comprising throttling means (66) for choking theexhaust of from said advanced position to said retracted position toforce air from said expansible air chamber through the restrictedexhaust of said motorto effect rapid deceleration of said rotor shaftand to prevent a substantial amount of air from being sucked into saidmotor, said return means (3) applying a retracting force to said statorequal to at least 30 pounds per square inch. 1 a

17. A portable grinder as defined in claim l6 wherein said stator .(4)has portions (til!) providing restricted exhaust passages adjacent theinternal cylindrical surface (35) of said housing'and said housing hasradial exhaust ports (15) which are closed by a portion (66) of thestator in response to retraction of the stator to stop rotation of therotorshaft in less than 1 second.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated ugust 311971 Patent No. 3 G02 315 Inventor(s) Herman L. 'luttle It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 7, line 7, the words "cut off" should read --cut off to force theair from said chamber through said air motor and out said exhaustmeans-. Column 8, line 18,

claim reference numeral "4" should read -ll-.

Signed and sealed this 28th day of March 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTI'SCHALK Commissioner of PatentsAttesting Officer USCOMM-DC 60875-0 09 "OHM 1 0-1050 (10-69)

1. A process of operating a portable air tool having a housing, a rotaryair motor in said housing having a stator, a rotor, a rotor shaftadapted to project from said housing, an inlet opening for admitting airunder pressure to said motor, and exhaust means for discharging theexhaust air from said motor, and means on said shaft for supporting agrinding tool, said process comprising admitting air to said inletopening and causing said rotor and said shaft to rotate at a speed of atleast 15,000 revolutions per minute, and cutting off the supply of saidhigh pressure air to said motor to discontinue operation of said motor,the improvement which comprises a. providing an expansible air chamberin communication with said inlet opening, b. expanding said air chamberto a predetermined volume, and c. contracting said air chamber to lessthan half such volume when the supply of said high pressure air to saidmotor is cut off while simultaneously throttling said exhaust means torestrict and resist the flow from said air chamber so as to effect rapiddeceleration of said rotor shaft and to prevent a substantial amount ofair from being sucked into said motor.
 2. A process as defined in claim1 wherein said chamber is expanded and contracted automatically by apiston means and yieldable elastic means which yieldably resistsexpansion of said chamber by movement of said piston.
 3. A process asdefined in claim 1 wherein said motor is mounted for reciprocation in ahousing and said chamber is expanded and contracted by axialreciprocation of said air motor.
 4. A process as defIned in claim 1wherein the air is admitted to said inlet opening at a pressure of 50 to150 pounds per square inch. 5 . A process as defined in claim 4 whereinthe contraction of said chamber reduces the speed of rotation of saidrotor shaft at least 10,000 revolutions per minute in a period of lessthan one second.
 6. A process as defined in claim 5 wherein said airmotor is operated at a speed of at least 20,000 revolutions per minutewhen such deceleration is initiated.
 7. A process as defined in claim 4wherein the force applied to contract said air chamber during suchdeceleration is equal to at least 25 pounds per square inch.
 8. Aprocess of operating a portable grinder having a housing, a rotaryexpansible chamber air motor in said housing having a stator, a rotor, arotor shaft having means supporting a grinding tool, inlet means foradmitting air under pressure to said motor, and exhaust means fordischarging the exhaust air from said motor, said process comprisingmounting said stator to slide axially in said housing between anadvanced operating position and a retracted position, whereby a closedexpansible air chamber is provided on one side of the piston like statorat the rear of said housing in communication with the inlet of said airmotor, supplying air to said air chamber at a pressure of 50 to 150pounds per square inch to cause high speed rotation of the grindingtool, and discontinuing the supply of high pressure air to said motorwhile simultaneously causing a rapid cushioned deceleration of saidgrinding tool, said deceleration being effected by throttling saidexhaust means to choke and restrict the flow of exhaust air from saidmotor and moving said stator rapidly from said advanced to saidretracted position to force the air from said expansible air chamberthrough the restricted exhaust of said motor to stop rotation of therotor shaft and to prevent a substantial amount of air from being suckedinto said motor.
 9. A process as defined in claim 8 where in theretracting force applied to said pistonlike stator to cause the rapiddeceleration is equal to a pressure of at least 25 pounds per squareinch.
 10. A process as defined in claim 8 wherein the grinding tool isdecelerated at a rate of at least 10,000 revolutions per minute persecond.
 11. A small portable air tool having a closed cylindricalhousing with a diameter of 1 inch to 2 inches and a length of 4 to 8inches adapted to be held in the hand of an operator, a rotaryexpansible-chamber air motor having a piston like stator mounted toslide axially in said housing between an advanced operating position anda retracted position, whereby an expansible air chamber is provided atthe rear of said housing, said air motor having inlet and exhaustopenings to admit air under pressure from said expansible chamber andexhaust it through the stator to atmosphere and having a rotor shaftmounted for rotation coaxial with said housing and a rotor carried bysaid shaft which is driven by the pressure of the air admitted to saidmotor, tool gripping means rigidly mounted on the end of said rotorshaft, control valve means for connecting the rear of said housing to asource of air under pressure having a normal closed position, in whichthe flow of air to said expansible chamber and said air motor is cutoff, and an open position, in which air is admitted to said chamber tomove the motor to its advanced position and to effect driving of themotor, and means for automatically causing a cushioned deceleration ofsaid air motor comprising throttling means for restricting the exhaustof the motor after said valve means is moved to the closed position andhigh-pressure spring return means for moving said stator rapidly fromsaid advanced position to said retracted position to force the air fromsaid expansible air chamber through the restricted exhaust of said motorto effect rapid deceleration of said rotor shaft anD to prevent asubstantial amount of air from being sucked into said motor.
 12. Aportable air tool as defined in claim 4 wherein said throttling meanschokes the flow of exhaust gas from said air motor in response to axialretracting movement of the air motor to stop rotation immediately.
 13. Aportable air tool as defined in claim 11 wherein said spring meansapplies a retracting force equal to at least 25 pounds per square inch.14. A portable air tool as defined in claim 13 wherein said means forcausing deceleration of said air motor causes deceleration of the rotorshaft at a rate of at least 10,000 revolutions per minute per second.15. A portable air tool as defined in claim 11 wherein said cylindricalhousing has exhaust ports which are located near the middle portion ofsaid pistonlike stator when the stator is in its advanced position andwherein said ports are closed in response to movement of the stator toits retracted position to choke the motor exhaust.
 16. A portablehigh-speed pneumatic grinder (A) having a closed housing (1) a rotaryexpansible-chamber air motor (B) having a piston like stator (4) mountedto slide axially in said housing between an advanced operating positionand a retracted position, whereby an expansible air chamber (2) isprovided at the rear of said housing, said air motor having inlet andexhaust openings (42 and 44) to admit air under pressure from saidexpansible chamber and exhaust it through the stator to atmosphere andhaving a rotor shaft (6) mounted for rotation coaxial with said housingand a rotor (5) carried by said shaft having sliding vanes (58) drivenby the pressure of the air admitted to said motor, means (8) on the endof said rotor shaft for gripping a grinding tool (7), control valvemeans (9) for connecting said housing to a source of air under pressurehaving a normal closed position, in which the flow of air to saidexpansible chamber and said air motor is cut off, and an open position,in which air under a pressure of 50 to 150 pounds per square inch isadmitted to said chamber to move the motor to its advanced position andto effect high-speed driving of the motor, and means for causing acushioned deceleration of said air motor to effect immediate stopping oftool rotation without causing damage to the grinding tool comprisingthrottling means (66) for choking the exhaust of the motor in responseto retraction of said stator after said valve means reduces the pressurein said air chamber and high-pressure return means (3) for moving saidstator rapidly from said advanced position to said retracted position toforce air from said expansible air chamber through the restrictedexhaust of said motor to effect rapid deceleration of said rotor shaftand to prevent a substantial amount of air from being sucked into saidmotor, said return means (3) applying a retracting force to said statorequal to at least 30 pounds per square inch.
 17. A portable grinder asdefined in claim 16 wherein said stator (4) has portions (68) providingrestricted exhaust passages adjacent the internal cylindrical surface(35) of said housing and said housing has radial exhaust ports (15)which are closed by a portion (66) of the stator in response toretraction of the stator to stop rotation of the rotor shaft in lessthan 1 second.